Mellman’s survey has a similar margin to a Boston Globe poll, released Sunday, which had Coakley up by 15 percent. But this new poll has the attorney general enjoying a wider lead than in some other internal Democratic data.

Still, by commissioning and then disclosing private polling showing Coakley with a significant lead, Democrats are attempting to send the message that they are both taking the race seriously and that the party’s 60-seat majority in the Senate is not threatened. With some public surveys showing a close race over the last week, Democrats in Boston and Washington have grown increasingly nervous about the January 19th election to fill the seat of the late Sen. Edward Kennedy.

While no professional Democrat believes — or at least will admit — that Coakley could actually lose, the public polls showing a competitive contest have amounted to a wake-up call, alerting senior officials to a race few had been paying attention to because of the state’s overwhelmingly liberal tilt.

But now progressive groups are sending additional resources to Coakley, the Democratic National Committee is dispatching a veteran press operative to Boston and party officials are paying for polls to assess whether she may actually have a close race on her hands.

A third-party candidate named Joseph Kennedy (no relation to the late senator) got 6 percent in Mellman’s poll. Nine percent of voters were undecided.

The data also reveal why some Democrats are urging Coakley to get more aggressive with Brown. The Republican nominee is viewed favorably by 48 percent of voters and unfavorably by just 25 percent, a reflection of not only how little known he is to voters but also the degree to which Democrats have not gone after him. By contrast, the better-known Coakley is viewed favorably by 56 percent of voters and unfavorably by 33 percent. According to the poll, there is also more enthusiasm for Brown than for Coakley.

National Republicans tracking the race declined to reveal their own internal poll numbers.

But a GOP strategist involved in the contest asked “If the Democrats honestly believe their lead is as strong as this poll suggests then why are they rushing staff, money and other resources up to Massachusetts?"